This invention relates to a process for preparing neodymium metal or neodymium metal alloys which can be advantageously used in processes for producing neodymium based permanent magnets.
Heretofore, no highly efficient method has been available for the formation of magnesium based rare earth alloys. A paper, Compt. rend., 217, 603, 1943, describes a metallothermic reduction of rare earth chlorides with magnesium, but produces products with rare earth concentrations in the area of 10 weight percent, making any further purification much more difficult.
Another prior art process described in Compt. rend., 220, 778, 1945, uses a liquid magnesium-cadmium cathode to make ternary alloys of rare earth-magnesium-cadmium. This results in having to remove two metals to obtain a pure rare earth metal, and prevents the recovery of pure magnesium. It also limits the cell construction to a bottom tapping cell.
Another prior art process described in Revue Chim. Miner, Vol. 10, 1973, pp 347-353, uses a molten pool cathode to make rare earth metals, but in this process a fluoride based system is used and oxide or fluoride salts are used for feed. The cell of this prior art process operates at higher temperatures such as 1000.degree. C. and has the environmental and health problems associated with fluorides.
One method in the present art for the preparation of neodymium metal or neodymium/iron alloy includes molten salt electrolysis of neodymium salts which operates either at low current efficiencies or involves the use of molten fluorides, which presents handling and safety problems.
Another method known in the prior art includes metallothermic reduction of neodymium salts, which involves the use of metallic calcium as the reducing agent and creates large volumes of slag for disposal.
It is desired to provide a method which uses much safer reactants, is operated as an entirely closed system, and provides no slag for disposal. It is also desired to provide a process which produces a pure magnesium as a by-product which is also a marketable product. It is further desired to provide an electrolytic process which overcomes the problem of the solubility of the product metal in the electrolyte of such process. A product which dissolves in the electrolyte is easily rechlorinated, causing low current efficiencies. By depositing the product metal into a second metal, the product is not soluble, and higher efficiencies are obtained.